It has long been known to provide computer workstations interconnected by digital communication networks whereby users of the individual workstations may communicate with one another over the network for tasks such as file serving from a host or server to client computers. This has been previously common, for example, by means of a typed note, data or program file transmitted to another user. More recently, users have increasingly requested multimedia file services, desktop conferencing, remote presentations, and other multimedia applications between network users. However, such multimedia applications utilizing data-intensive sound, voice, and video flows require performance guarantees for high disk access and high bandwidth communication links between distributed computing systems with minimal communication delay, maximum throughput, and instantaneous burst communication capability. As a result, it has become very difficult to schedule appropriate resources to meet the requirements of such multimedia applications.
Prior art has recognized that certain data in a network, such as that associated with multimedia, may require priority handling. Thus, for example, a "quality of service" (QOS) or bandwidth has been defined in the literature. Quality of service or bandwidth seeks to describe various parameters which may be specified in an attempt to define certain minimum requirements which must be met for transmission of given data types over the network. See, for example, quality of service standards set forth in the OSI TP4 Open System Interconnect Standard X.214 and the quality of service standards defined in CCITTQ.931 (ISDN), Q.933 (frame relay), and Q.93B (B-ISDN ATM) drafts. As yet another example there is an architected priority mechanism in the IEEE 802.5 Token Ring. A station on the ring with a high priority frame to send may indicate this in an access control field of a passing frame. When a station sending the frame releases the token, it releases the token at the priority of the AC field, and eventually sets it back to its original priority as specified in an IEEE 802.5 medium access control protocol. The IEEE standard and implementations thereof merely specify a protocol for increasing and decreasing priority. However, the user of such a service, such as a client-server file system, has to determine when service guarantees are needed for certain file accesses. For example, multimedia file reads for playing sound, voice, and video from a server to a client need certain quality of service guarantees.
Allocating resources when a connection is made between digital computers, such as for a client-server session, is known where memory is allocated to hold information related to the session. Buffers are also commonly reserved for file access on computers, such as on a server computer. Buffers may also be reserved on the client computer for multimedia file where a memory buffer must be large enough to store a reserve of file elements so that variations in delay between the server and client are absorbed. That is, there should be enough file elements stored in the memory buffer so that the buffer will not go empty during the playback of sound, voice or video. Otherwise, a glitch or jitter will occur causing a deterioration in the quality of a presentation. For example, if the maximum delay is two seconds and the multimedia flow averages 150 kilobytes per second, then a buffer at least 300 kilobytes in size is needed to preserve quality of service.
Many types of files contain information in their header useful for determining such quality of service parameters. Other types of files may require that the file be read, parsed or scanned to determine such quality of service parameters. However, in a general purpose client-server environment, a very large variety of file types and formats exist and a file server may not be programmed to determine quality of service parameters in all cases. In addition, an application program, running on a workstation in a client-server environment, may not recognize whether a file being accessed is located on the workstation or on a remote file server. If the file is located on the application program workstation, then quality of service is generally met. However, if the file being accessed is located on a remote server, then the file access must contend for server resources such as disk cycles or bandwidth, disk controller cycles, system bus resources, server processor resources, and network resources. As a result, it is difficult to maintain quality of service in a client-server environment for remote file accesses.